Patent GB-1055629-A (GB)
Title: Improvements in and relating to associative memory systems
IPC: G11C15/06
Filed: 1963-12-30
Abstract: 1,055,629. Digital data storage apparatus. GENERAL ELECTRIC CO. Dec. 30, 1963 [Jan. 2, 1963], No. 51170/63. Heading G4C. An associative memory system comprises means for interrogating the memory with a plurality of interrogation words in succession and means for selecting memory words which either match all or match at least one of the interrogation words. The selected words can then read out or processed in turn. The system described may be employed in five principal ways: (1) as a normal associative memory; (2) for selecting those words matching all of a succession of interrogation words; (3) for selecting those words matching at least one of a succession of interrogation words; (4) for selecting all the words of a block of words in the memory when only the first and last words of the block contain block-identification data; (5) for selecting the words within selected blocks, which words match all of a succession of interrogation words. The memory described is a cryotron matrix store. Constructional details.-The system described employs basic cryotron cells (Fig. 1, not shown) and basic memory elements (Fig. 2, not shown) as disclosed in Specification 1,053,770, each memory element, such as 70(1)(1), Fig. 5A, comprising a loop containing cryotrons 22<1>, 23<1>, 24<1> in which a " 1 is represented by a clockwise current and an "0" by an anticlockwise current. The memory comprises an m x n matrix array of elements 70(1)(1)- 70(m)(n), each row containing a write line 76(1) and a read line 78(1), these lines being combined at 80(1) to form a common read/write line 81(1). Each row contains also an " associative " line 77(1) and a shunt line 79(1), the arrangement being such that when interrogating digit currents are applied to all or a group of the inputs 91(1)-91(n), the current from terminal 85 remains flowing in the associative line 77(1) only if each applied digit matches the corresponding stored digit. Otherwise the current is diverted to the shunt line 79(1). The input current at 85 flows rightward along one of the lines in the first row, via a " fill-up " circuit 72(1), Fig. 5B, a set of " transfer " circuits 73(1), a "selection " flip-flop 75(1) via input and output terminals 86(1) and 87(1), a " match-indicating " flip-flop 74(1) via input and output terminals 88(1) and 89(1), to a terminal 89(2) in the second row, thence via the corresponding circuits of the second row and leftwards along the second row, subsequently through all the rows of the matrix the current return being at 90, Fig. 5B. Operational modes. (1) Normal associative search.-Initially, an input pulse on a line 94 renders the row shunt lines resistive so the current flows through the row associative lines. Appropriate interrogation currents are now applied to the group of column lines 91(1) in which it is desired to make a search, the row currents being switched to the shunt lines except where a match (successful comparison) is achieved. Current pulses are now applied to transfer lines 102, 103, Fig. 5B, the current on line 102 causing the match-indicating flipflop 74(1) in each matched row to be set thereby enabling such rows for selection, the current on line 103 ensuring that the flip-flops 74(1) of the other rows are reset. The selection operation is now performed by applying a current pulse to line 109. Assuming that flip-flop 74(1) in the first row is set, the gate of cryotron 110 is resistive so that the current on line 109 is steered through the control of a cryotron 113 thereby setting flip-flop 75(1) to cause the gate of a cryotron 108 to become superconductive thereby enabling the read-write line 81(1) of the first row so that a read or write operation can be performed. A second select current pulse on line 109 for selecting the next enabled row is effective to render the gate of cryotron 116 resistive thereby resetting flip-flop 75(1). (2) Succession of searches with AND connective.-In this mode of operation a succession of interrogations on different groups of columns is effected the final selection being of those rows which produced a successful match on all of the interrogations. As in (1), the memory is preset by a current applied to a line 94. Each interrogation is effected by applying current to the desired column lines 91(1)- 91(n). A transfer current is applied after each interrogation to line 103 only thereby resetting the flip-flop 74(1) of any row where it has remained set as the result of previous successful interrogation if the interrogation just made is not successful. Thus at the end of the operation only those flip-flops 74(1) remain set in rows which match all the applied interrogation words. (3) Succession of searches with OR connective.- After each interrogation a current is applied to transfer circuit line 102 (instead of 103) so that the match indicating flip-flop 74 of each row in which there is a match is set. Thus at the end of the operation all those flip-flops 74 will be set in which there has been a match of any of the interrogation words with the corresponding stored words. (4) Block search.-The memory may store blocks of data in which the block-identifying words are stored in the first and last rows only of the block, but all the rows of the block are to be selected if the interrogation word matches the block-identification words. For this purpose, " fill-up " circuits 72(1), Fig. 5B, are provided, one for each row. In operation, a preset pulse is applied to line 94 to cause all row currents to flow in the associative lines. The required digit interrogation currents are then applied to the appropriate column lines 91(1)-91(n). Assuming that rows 1 and m of the matrix contain the block identifying words, the operation is as follows. Assuming that the stored block provides a successful interrogation, the row current flows in associative lines 77(1) and 77(m) in rows 1 and m and in the shunt lines 79(2) &c. in the intermediate rows. A " fillup " current is now applied to line 50(1), Fig. 5B, and since the current in row 1 is in line 77(1), the " fill-up " current is diverted to a line 55(1) and sets match-indicating flip-flop 74(1) by means of cryotron 56(1), the "fill-up" current then passing via junction 61(2) in the second row and cryotron 56(2) to set the matchindicating circuit in the second row, and similarly in the subsequent rows until it reaches row m when it passes via cryotron 64(m) to set the match-indicating flip-flop of row m. If the " fill-up " current were to pass to further storage rows it would flow along lines corresponding to 59(1) in row 1 and the corresponding match-indicating flip-flops would not be set. (5) By combining the interrogation described at (2) and (4)- above, a succession of searches connected by the AND connective can be effected within selected blocks. Various other logical combinations of the described interrogations can be effected.